For some reason when I have 3 parts condensed into 1 stave (like Clarinet, Trumpet or Trombone) and I have 2 parts on a lower octave and the top part on a higher octave I get multiple note heads instead of the “2 3 a2”. This hasn’t happened with any other harmony that I’ve tried. Is this a bug? Why is this happening? How can I fix this?
No, it is not a bug. That does not mean it is attractive nor the only way such things have been notated, but this is one form of standard notation in the circumstances shown.
The workaround is to change the condensing strategy for that stave while in ‘Engrave’ mode. You’ll likely need to quickly reset the condensing to default, otherwise you might not like the results.
If there’s an option to show multiple stems there, try that. It would properly solve the issue. (I don’t know if this is possible off the top of my head; I haven’t had cause to mess with condensing very much.)